1. Field of the Invention
The present invention is generally related to photolithography systems and, more particularly, to maintaining a purged optical path in a photolithography system with a non-contact scavenging gas seal.
2. Related Art
In the fabrication of integrated circuits, photolithographic and projection printing techniques are used. In photolithography, an image contained on a reticle is projected through an optics system onto a surface of a semiconductor wafer. The semiconductor wafer surface is coated with photosensitive resist so that an image is etched thereon.
Generally, a photolithography system is located in an ambient atmosphere, clean room environment. However, some wavelengths of light used in photolithography are sensitive to absorption by atmospheric oxygen. Hence, when such oxygen-sensitive light wavelengths are used in photolithography, they must be transmitted through an oxygen-purged atmosphere.
In some situations, the ambient atmosphere of the clean room cannot be purged of oxygen because this causes problems with maintainability and service. Stages of the lithography system controlling motion of an illuminating laser across a semiconductor wafer surface may be controlled by a laser interferometer. The laser interferometer is sensitive to the index of refraction of light of air, which may be affected by random index of refraction fluctuation induced by ambient nitrogen concentration fluctuation. Hence, in some situations, the nitrogen-purge environment must be restricted as much as possible to the lithography system""s optical path.
Sealing the optical path, however, is difficult because the optical path may have multiple points needing to be sealed from the ambient environment.
Furthermore, a seal may be required between surfaces in the optical path that move relative to each other. For instance, the projection optics may move in relation to the semiconductor wafer surface when projecting light wavelengths across different areas of the semiconductor wafer surface. The projection optics may also move in relation to the reticle when different areas of the reticle are being imaged. What is needed is a method and apparatus for maintaining an oxygen-purged optical path in a lithography system.
The invention is directed to a method and apparatus for a non-contact scavenging gas seal. The invention is further directed to method and apparatus for providing a purged optical path between an optical source surface and an optical target surface and for permitting relative movement between the optical source surface and the optical target surface. The non-contact scavenging gas seal of the present invention is formed by a scavenger. The scavenger is located in the optical path between the optical source surface and the optical target surface.
The scavenger apparatus includes a body, a central cavity, one or more gas supply bores, and one or more gas removal bores. The body defines first and second opposing surfaces. The first opposing surface is configured for positioning closely adjacent to the optical target surface. The second opposing surface is configured to mate with the optical source surface. The central cavity is formed in the body for passing light through the body, the central cavity being open at the first and second opposing surfaces. The one or more gas supply bores are formed in the body for supplying a flow of a purge gas to the central cavity. The one or more gas removal bores are formed in the body at the first opposing surface to remove gas from a gap formed between the first opposing surface and the optical target surface.
Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the left-most digit(s) in the corresponding reference number.
FIG. 1 illustrates a block diagram of a conventional lithography system.
FIG. 2 illustrates an exemplary block diagram of a lithography system, according to an embodiment of the present invention.
FIG. 3 illustrates a cross-sectional view of an exemplary non-contact scavenging gas seal, according to an embodiment of the present invention.
FIG. 4 illustrates a perspective view of an exemplary scavenger, according to an embodiment of the present invention.
FIG. 5 illustrates an exemplary movable surface, according to an embodiment of the present invention.
FIG. 6 illustrates a bottom view of an exemplary scavenger, according to an embodiment of the present invention.
FIG. 7 illustrates a cross-sectional view of a non-contact scavenging gas seal, incorporating the exemplary scavenger of FIG. 6.
FIG. 8 shows a flowchart providing detailed operational steps of an example embodiment of the present invention.